Make sure you are allowed a gun in your home. I didn't have a dorm, but those that did weren't allowed to have guns. Heck, you weren't allowed car parts in the dorms and this was NADC. The dorms themselves were a shady place to be. Violence and drugs are common. There was such a fear of rape that no females were allowed there and the female students have their own little building and every woman's bathroom was locked and only female students had a key. Just being at the campus at night was scary, but after class I was never alone till I got to my apartment. I'm a big guy and I'm afraid of much but I never felt comfortable in Nashville.
If the rules allow guns, then if I was in that situation, I'd use #2 or possibly a low recoil 2 3/4 slug. The purpose of the low recoil would be to reduce over penetration and not go through walls as easy.